The invention relates generally to the manufacture of semiconductor devices. More particularly, the invention relates to a non-solvent system for semiconductor wafer processes such as removing the edge bead formed during spin coating processes.
Coating materials such as photoresist are typically applied to a semiconductor wafer by flowing liquid coating material onto the top surface of the wafer while it is spinning. The wafer is held on a disk shaped, rotating spin chuck. The diameter of the chuck is slightly less than the diameter of the wafer. The chuck is positioned so that the wafer lies on the chuck in a level horizontal plane. In operation, the backside or inactive surface of the wafer is placed onto the chuck. The chuck applies a suction to the backside of the wafer to hold the wafer in place on the chuck. The chuck is rotated by a motor-driven axle that extends down from the chuck. As the wafer is rotated on the chuck, liquid photoresist material is applied to the center of the wafer. The photoresist spreads radially outward from the center of the wafer towards the edge to coat the top of the wafer. Ideally, all excess coating material is ejected from the edge of the wafer. In practice, however, some excess photoresist tends to collect at and form a bead along the edge of the wafer.
Processes to remove the edge bead are known. Typically, a solvent is dispensed along the edge of the wafer to dissolve the edge bead and remove the resist from the extreme edge of the wafer. If necessary, the coating is exposed to light prior to contact with the solvent, or developer in order to develop the coating and render it soluble in the solvent. The solvent may be dispensed through a nozzle directed toward the backside edge of the wafer, in which case it wicks up around to the top of the wafer to dissolve the edge bead, or the solvent may be dispensed directly onto the top edge of the wafer. In either case, the process allows solvent and dissolved photoresist to be splashed about and often leaves a jagged edge profile on the photoresist or other coating material. In the process of U.S. Pat. No. 5,952,050, the method includes the steps of dispensing a solvent selectively onto the edge of the wafer to dissolve the coating material at the extreme edge of the wafer, and applying a suction to vacuum excess solvent and dissolved coating material from the wafer.